This invention relates to a refrigerant heating type heating apparatus which heats an evaporator of the refrigeration cycle by means of a burner, and discharges the heat in a room by using a condenser thereby heating the room.
Conventionally, a heating apparatus of this type comprises a refrigeration cycle constructed by connecting a compressor, a condenser, refrigerant flow rate adjusting means, and an evaporator in a circuit, an indoor fan located near the condenser, and a gas burner provided near the evaporator to heat it. A fuel gas is supplied to the gas burner from a fuel gas source. The evaporator is installed in or on a housing for guiding the combustion gas of the burner.
The compressor, when it is driven, discharges a high-temperature gas refrigerant. This refrigerant serves for the heating operation as it circulates passing through the condenser, flow rate adjusting means and evaporator. In the heating operation, when the gas burner is ignited, the combustion gas of the burner flows through the housing, thus heating the evaporator. When the refrigerant is evaporated in the evaporator, is absorbs a large amount of heat. This latent heat is radiated into a room when the refrigerant condenses in the condenser, thereby heating the room.
In a heating apparatus constructed as described above, the combustion rate of the gas burner in the heating operation is controlled by an indoor command that is determined in accordance with an optionally set temperature and an actual room temperature detected by a room temperature sensor. At the same time, the flow rate adjusting means is controlled such that an outlet temperature of the evaporator to be heated or the difference between the outlet temperature and an inlet temperature of the evaporator has a predetermined value.
However, in a heating apparatus operated under the above-mentioned control system, water vapor contained in the combustion gas condenses on the inner surfaces of the housing, particularly, when the room temperature is low and the combustion rate of the burner is small. The condensation water corrodes the housing and evaporator, thus decreasing durability of the heating apparatus.